Lead-free piezoelectric materials having a piezoelectric performance equivalent to that of lead zirconate titanate (PZT), which contains a large amount of lead that is harmful to human body, have been developed as a substitute for PZT. In recent years, a lead-free piezoelectric material containing barium titanate has been proposed, as described in PTL 1. However, barium titanate has a crystal structure that undergoes phase transition at a temperature close to room temperature (about 5° C.) Therefore, the piezoelectric performance of a piezoelectric element including barium titanate varies in accordance with variation in the ambient temperature. As a result, there is a problem that electric power consumed to cause a certain piezoelectric displacement differs by a large amount depending on the ambient temperature.
PTL 2 proposes a technology regarding a drive circuit of an ultrasonic motor. In the drive circuit described in PTL 2, a capacitor is arranged parallel to the ultrasonic motor, so that variation in clamped capacity of the ultrasonic motor is canceled in a temperature range higher than room temperature.